Adhesives are often used in the manufacture of various composite articles such as the component parts of automobiles, airplanes, and watercraft. Various adhesives are known for these purposes including, Robins et al., U.S. Pat. No. 4,668,736 which discloses an epoxy resin composition comprising a room temperature curable glycidyl ether epoxide group-containing material, an amino-terminated aliphatic polyether curing agent, a polymeric toughening agent, and a metal salt catalyst. Robins requires a specific catalyst to promote curing at commercially practicable rates with a limited open time.
Sanders et al., U.S. Pat. No. 5,151,470 discloses epoxide resins comprising aminocrotonates, useful as curing agents within the adhesive composition and which also provide flexibility to the cured bond. Read et al., U.S. Pat. No. 5,034,251 discloses a mixture of substantially solid particles of a first reactive component, which may include a polyfunctional epoxy, with separate substantially solid particles of at least a second reactive component and a water soluble polymeric binder having substantially no hydroxyl groups. However, Read et al. requires the use of a catalyst to promote accelerated cure and also require a water soluble polymeric binder.
M ulhaupt et al., U.S. Pat. No. 5,030,698 discloses heat curable compositions which may be a one-part adhesive system comprising an epoxy resin, a curing agent for the resin, a liquid copolymer based upon ethylenically unsaturated comonomers such as butadiene or acrylonitrile, and, a selected segmented copolymer of recurring soft segments containing polypropylene glycol units or polybutylene glycol units. Speranza et al., U.S. Patent No. 5,030,710 discloses Polyamide cured nylon-6 non-adhesive articles produced by a combination of one or more carboxylic acids combined with a glycol diamine such as triethylene or tetraethylene glycol diamines.
Dearlove et al., U.S. Pat. No. 4,383,060 discloses an epoxy adhesive useful for structurally bonding automotive body panels and in the manufacture of making these panels from sheet molding compound. The Dearlove et al. composition uses a monofunctional epoxy to provide flexibility to the adhesive bond once formed.
In the fabrication of various component parts, the manner in which the individual components are assembled must often be considered in view of the entire manufacturing process. For example, operational electrical and mechanical components must be affixed and held in place with mechanism which will effectively withstand the further processing subjected to the assembly such as a car. Further, the structural components such as body panels including joints, prelaminated multipiece panels, and flanges must all be attached keeping in mind that the final assembly may need to be heated in order to affix, prime, or paint a portion of the structure or the structure as a whole.
For example, induction curing of hem-flange joints is well-known assembly in the automotive industry. Generally, a "hem-flange" joint is an assembly or a manner in which two or more metal pieces are processed or otherwise bonded to make a joint. For example, when bonding two pieces of metal to make a hem-flange joint, one piece of metal is retained as a protruding or a projecting flange. The second piece of metal which may be incident to the first piece of metal at any number of angles. Generally the second piece of metal is bent or otherwise folded to form a pocket or "hem" which envelopes both sides of the metal flange. An adhesive is commonly inserted into the hem and sandwiches, surrounds or covers both sides of the flange as inserted into the hem and when subsequently cured, forms a bond.
One example of a hem flange joint may be found in the hood for the engine compartment of an automobile. Generally, for example, a metal hood piece will comprise a peripheral hem flange joint which serves to secure various composite layers to the underside of the hood. The joint must retain strength and flexibility to withstand the continual vibration, impact, and other severe environmental stresses, such as heat, to which vehicle components are subjected.
Along with other problems, the common use of metal lubricants, the temperature sensitivity of component parts, as well as the accessibility of these parts during processing, are among the factors which have presented problems in the formation of hem-flange joints.
Generally, one-part epoxies are used for such applications which can cure in about 5 seconds at temperatures in the range of approximately 375.degree. to 425.degree. F. However, as pressure to reduce vehicle weight has increased, thin gauge metals are being used more frequently. Thin gauge metals often warp at the higher temperatures needed to cure the single-phase standard induction cure epoxies.
Another type of adhesive often used in the assembly of operational and structural components of automobiles comprises a two-part room temperature curing acrylic epoxy adhesive. This adhesive cures in about 30-40 minutes at 70.degree. F. but require significantly longer cure times at 40.degree.-50.degree. F. Further, this adhesive generally cannot be rapidly induction cured because of the high volatility of its acrylic components. As a result, any temperature fluctuation may create severe problems in manufacturing processes due to the temperature dependence of the cure mechanism in this adhesive composition. For example, bonding cold metal panels during the winter months may be a problem with the acrylic/epoxy adhesive.
As a result, there is a need for toughened epoxy adhesive with the physical properties necessary to create bonds of high structural integrity and attach operational and structural components in heavy assemblies such as automotive, aircraft, and water vehicle manufacture without the creation of defects in the assembly.